The present invention relates generally to disc drive data storage systems. More particularly, the present invention relates to controlling the vibration of a piezoelectric microactuator in a disc drive.
A typical disc drive includes one or more magnetic discs mounted for rotation on a hub or spindle. A typical disc drive also includes one or more transducers supported by a hydrodynamic air bearing which flies above each magnetic disc. The transducers and the hydrodynamic air bearing are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to retrieve information from the magnetic discs and to store information on the magnetic discs.
An electromechanical actuator operates within a negative feedback, closed-loop servo system. The actuator moves the data head radially over the disc surface for track seek operations and holds the transducer directly over a track on the disc surface for track following operations.
Information is typically stored on the magnetic discs by providing a write signal to the data head to encode flux reversals on the surface of the magnetic disc representing the data to be stored. In retrieving data from the disc, the drive controller controls the electromechanical actuator so that the data head flies above the magnetic disc, sensing the flux reversals on the magnetic disc, and generating a read signal based on those flux reversals. The read signal is then decoded by the drive controller to recover the data represented by flux reversals stored on a magnetic disc, and consequently represented in the read signal provided by the data head.
Accurate positioning of the data head over a track on the disc is of great importance in writing data to the disc and reading data from the disc.
In prior systems, servo operations were accomplished based on a dedicated servo head. In a dedicated servo type of system, servo information is all written to one dedicated surface of a disc in the disc drive. All of the heads in the disc drive are mechanically coupled to the servo head which is used to access the servo information. Thus, all of the heads in the dedicated servo disc drive are positioned based on the servo information read from the servo surface. This type of system allows the disc drive to conveniently execute parallel read and write operations. In other words, with appropriate circuitry in the drive controller, read and write operations can be executed in parallel using a plurality of the data heads mounted on the actuator, the data heads being simultaneously positioned based on the servo information read from the dedicated servo surface.
However, track densities on magnetic discs have been increasing for many years. Increased track densities on the magnetic disc require more accurate and higher resolution positioning. The mechanical offset between heads in a dedicated servo system can exceed one track width. Thus, the industry has seen a shift to embedded servo information in certain applications.
In an embedded servo system, servo information is embedded on each track on each surface of every disc. Thus, each data head returns a position signal independently of the other data heads. Therefore, the servo actuator is used to position each individual data head while that particular data head is accessing information on the disc surface. The positioning is accomplished using the embedded servo data for the track over which the data head is then flying.
Microactuated suspensions have been proposed in order to allow fine position control of the read/write head in an embedded servo system. A piezoelectric microactuator finely adjusts the position of a read/write head relative to a given track in response to a provided electrical signal. The usage of a piezoelectric microactuator will naturally result in additional resonances being introduced into the system. This will not present a serious problem when it is possible to sense and feedback the position of the read/write transducer and use the microactuator itself to compensate for the additional mechanical resonances. However, in certain models of disc drive operation it is either not possible to sense and feedback the read/write transducer position or the servo algorithm is not naturally a position error feedback system.
This problem presents itself when the disc drive is being track written. During the servo track writing operation, there is generally no measurement of the actual head position. Rather, the head position is inferred by measuring motion of some point on the actuator arm and assuming that the arm/suspension is a rigid body. The rigid body assumption does not hold true if the microactuator resonates, and if the microactuator does resonate then it will result in an increase in the written-in error on the servo tracks.
This problem also occurs during seek and settle operation of the disc drive. During seek the servo algorithm generally controls the velocity of the read/write transducer. In this mode it is critical that the suspension be very rigid so that xe2x80x9cringingxe2x80x9d of the read/write transducer does not occur. The use of a microactuator results in a suspension that is less rigid than a suspension without a microactuator.
The present invention provides a solution to this and other problems and offers other advantages over the prior art.
The present invention relates to controlling the vibration of a piezoelectric microactuator in a disc drive.
One embodiment of the present invention is directed to a method for controlling vibration of a piezoelectric microactuator in a disc drive. The mechanical strain on the piezoelectric microactuator is sensed and an electrical signal is applied to the piezoelectric microactuator based on the sensed strain. Applying the electrical signal to the piezoelectric microactuator produces a mechanical force on the microactuator which counteracts the sensed strain.
In one embodiment, the strain on the piezoelectric microactuator is sensed by sensing a voltage across the piezoelectric microactuator and then separating the voltage across the piezoelectric microactuator into a voltage externally applied to the piezoelectric microactuator and a voltage induced on the piezoelectric microactuator by mechanical strain. An electrical signal is then applied to the piezoelectric microactuator based on the voltage induced on the piezoelectric microactuator.
Another embodiment of the present invention is directed to a disc drive including a disc, a head, a piezoelectric microactuator, a strain sensor and a controller. The disc is capable of storing data. The head is capable of being positioned adjacent the disc and of reading and writing data to the disc. The piezoelectric microactuator finely positions the head relative to the disc. The strain sensor is capable of sensing the mechanical strain on the piezoelectric microactuator and of producing a sensed strain signal that is indicative of the sensed strain. The controller is capable of receiving the sensed strain signal and applying an electrical signal to the piezoelectric microactuator based on the sensed strain. The electrical signal applied to the piezoelectric microactuator produces a mechanical force on the microactuator which counteracts the sensed strain.
In a further embodiment, the strain sensor includes a bridge circuit that is coupled to the piezoelectric microactuator. The bridge circuit is capable of sensing a voltage across the piezoelectric microactuator and of separating the voltage across the piezoelectric microactuator into a voltage externally applied to the piezoelectric microactuator and a voltage induced on the piezoelectric microactuator by mechanical strain.